jhash.h

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/* jhash.h: Jenkins hash support.
 *
 * Copyright (C) 1996 Bob Jenkins (bob_jenkins@burtleburtle.net)
 *
 * $Id: jhash.h 2738 2007-02-17 13:59:56Z regit $
 *
 * http://burtleburtle.net/bob/hash/
 *
 * These are the credits from Bob's sources:
 *
 * lookup2.c, by Bob Jenkins, December 1996, Public Domain.
 * hash(), hash2(), hash3, and mix() are externally useful functions.
 * Routines to test the hash are included if SELF_TEST is defined.
 * You can use this free for any purpose.  It has no warranty.
 *
 * Copyright (C) 2003 David S. Miller (davem@redhat.com)
 *
 * I've modified Bob's hash to be useful in the Linux kernel, and
 * any bugs present are surely my fault.  -DaveM
 */

#ifndef _JHASH_HEADER
#define _JHASH_HEADER

#include <stdint.h>

/* NOTE: Arguments are modified. */
#define __jhash_mix(a, b, c) \
{ \
  a -= b; a -= c; a ^= (c>>13); \
  b -= c; b -= a; b ^= (a<<8); \
  c -= a; c -= b; c ^= (b>>13); \
  a -= b; a -= c; a ^= (c>>12);  \
  b -= c; b -= a; b ^= (a<<16); \
  c -= a; c -= b; c ^= (b>>5); \
  a -= b; a -= c; a ^= (c>>3);  \
  b -= c; b -= a; b ^= (a<<10); \
  c -= a; c -= b; c ^= (b>>15); \
}
/* The golden ration: an arbitrary value */
#define JHASH_GOLDEN_RATIO      0x9e3779b9

#ifdef USE_JHASH3

static uint32_t jhash_3words(uint32_t a, uint32_t b, uint32_t c,
                             uint32_t initval)
{
        a += JHASH_GOLDEN_RATIO;
        b += JHASH_GOLDEN_RATIO;
        c += initval;

        __jhash_mix(a, b, c);

        return c;
}
#endif                          /* USE_JHASH3 */

#ifdef USE_JHASH2

/* A special optimized version that handles 1 or more of uint32_ts.
 * The length parameter here is the number of uint32_ts in the key.
 */
static inline uint32_t jhash2(uint32_t * k, uint32_t length,
                              uint32_t initval)
{
        uint32_t a, b, c, len;

        a = b = JHASH_GOLDEN_RATIO;
        c = initval;
        len = length;

        while (len >= 3) {
                a += k[0];
                b += k[1];
                c += k[2];
                __jhash_mix(a, b, c);
                k += 3;
                len -= 3;
        }

        c += length * 4;

        switch (len) {
        case 2:
                b += k[1];
        case 1:
                a += k[0];
        };

        __jhash_mix(a, b, c);

        return c;
}
#endif                          /* USE_JHASH2 */

#endif

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